<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    .outer {
        height: 300px;
        position: relative;
    }
    .left{
        /*占据*/
        position: absolute;
        width: 100px;
        /*left: 0;*/
        height: 100%;
        background-color: blue;
    }
    .right{
        position: absolute;
        right: 0;
        top: 0;
        width: 100px;
        height: 100%;
        background-color: lime;
    }
    .mid {
        height: 100%;
        /*position: absolute;*/
        /*left: 100px;*/
        /*right: 100px;*/
        margin-left: 100px;
        margin-right: 100px;
        background-color: pink;
    }
</style>
<body>
<div class="outer">
  <div class="left"></div>
  <div class="mid"></div>
  <div class="right"></div>
</div>
</body>
</html>
